1. Field of Invention
This invention is a bioreactor that can support a large fixed microbial or autotrophic biofilm that consumes soluble organic or inorganic substrates while producing a nutrient rich biomass and gases such as hydrogen, oxygen, biofuels, and ammonia, that are harvested for a beneficial purpose. This invention can be applied to a variety of processes for recovering valuable gases, nutrients, and products produced from different substrates by autotrophic organisms in a single reactor without the use of chemicals and with minimal energy inputs. Applications include nutrient removal and harvesting from a variety of water bodies, volatile or semi-volatile gas stripping, concentration of stripped gases, and compost biogenic drying.
2. Background
Nutrients discharged from agricultural operations, waste management, and bioenergy processing facilities are significant environmental problems adversely affecting over 30% of our nations waters. The National Academy of Engineering of the National Academies recently published the “Grand Challenges for Engineering,” posted at http://www.engineeringchallenges.org/_cms/challenges.aspx. One of the 14 challenges was “Manage the Nitrogen Cycle”. The “nitrogen issue” is the result of twice as much nitrogen being introduced into the world through anthropogenic sources as introduced from natural sources. The ability to produce reactive nitrogen through the Haber-Bosch process has enabled man to feed the world. However, that engineering miracle has totally distorted the nitrogen cycle leading to significant environmental and public health problems. Seventy five percent of the additional anthropogenic reactive nitrogen input is converted to N2 gas through denitrification, a process that converts a portion (2% to 6%) of the nitrogen to the powerful greenhouse gas N2O, which has an atmospheric lifetime of over 100 years. Aside from being a powerful GHG at 310 times CO2, N2O is now the primary cause of stratospheric ozone depletion. The remaining 25% of the added reactive nitrogen is accumulated in the soils, groundwater, rivers, estuaries, and oceans modifying those terrestrial and aquatic environments. The adverse impacts of nitrogen include the production of fine particulate matter that is responsible for atmospheric haze and increased human mortality, increased nitrate levels in groundwater, acidification of surface water, harmful toxin producing algae blooms, hypoxia in coastal waters, forestry decline, and loss of terrestrial biodiversity.
Solutions to the “nitrogen problem” have primarily been through the use of engineered denitrification systems that increase the NOx, N2O, and fine particulate matter emissions to the atmosphere. Some processes attempt to recover and reuse ammonia and thereby reduce the industrial production of ammonia through the Haber-Bosch process. Ion exchange, membrane separation, and stripping technologies have all been used. The recovery processes invariably sequester the ammonia as dilute acidic solutions of ammonium sulfate or ammonium nitrate. Those processes have been shown to be uneconomical technologies.
Soluble phosphorus and nitrogen are the primary concern. Technology is required to economically remove soluble nitrogen, phosphorus, and potassium nutrients discharged from waste treatment, agricultural fields, or bioenergy facilities. Such facilities include manure management, food processing, wastewater treatment, and renewable energy production such as anaerobic digestion where a majority of the particulate organic nutrients are converted to soluble ammonia and phosphate.
A large variety of expensive technologies have been developed to remove both soluble nitrogen and phosphate from wastewater streams. Phosphate removal by chemical precipitation, biological assimilation, or crystallization (MAP, struvite) precipitation is expensive. Ammonia nitrogen removal by stripping, biological nitrification/denitrification, ammonia oxidation (Anammox) or precipitation as ammonium sulfate, nitrate, or phosphate is also expensive. Wetlands or constructed marshes are the least expensive but occupy large tracts of land where nutrient accumulation may not be sustainable.
Conversion of soluble nutrients to particulate matter, such as micro and macro algae is an attractive method for removing soluble nutrients. However, the limited productivity, ammonia toxicity, and cost of harvesting have prevented widespread adoption. Algae or cyanobacteria growth is limited by the turbidity that such growth imparts to the liquid. Light penetration is reduced in direct proportion to the algae biomass concentration. Pond surface area also limits CO2 transfer to the growing algae thereby limiting productivity. Variable depth and energy consuming gas injection photobioreactors have been proposed to overcome such limitations.
Ammonia toxicity is also a significant problem requiring dilutions of up to 20 to 1 for anaerobic digestate. Ammonia concentrations exceeding 100 ppm are inhibitory to autotrophic growth. Nitrogen loss to the atmosphere is also a significant problem in high pH systems. The loss of nitrogen to the atmosphere led the National Academy of Science to conclude that the growth of algae for biofuel production was unsustainable. “The estimated requirement for nitrogen and phosphorus needed to produce algal biofuels necessary to meet 5% of US transportation fuel ranges from 6 million to 15 million metric tons of nitrogen and from 1 million to 2 million metric tons of phosphorus if the nutrients are not recycled or included and used in co-products. Those estimated requirements represent 44 to 107 percent of the total nitrogen use and 20 to 51 percent of total phosphorus use in the United States.”
Finally, harvesting a highly concentrated biomass containing the recovered nutrients is expensive. The algae biomass separation and concentration is the most expensive unit process, representing 20 to 30% of the total cost of algae production and recovery systems. The limited productivity results in slow nutrient recovery in larger than desired reactors. Additional equipment for biomass nutrient separation and concentration increases the cost considerably.
The autotrophic rotating photobioreactor (RPB) is similar to the heterotrophic rotating biological contactor (RBC), a waste treatment device used to support large heterotrophic bacterial populations for the enhanced removal of soluble organic waste constituents flowing through the RBC. In fact, a rotating bioreactor contactor can be converted into a rotating photobioreactor by adding to it a light source directed at the microorgisms, using autotrophic micoorganisms, and providing a carbon source, such as carbon dioxide or bicarbonate. A variety of configurations and devices exist for heterotrophic waste treatment. The following U.S. patents are representative of the development of the art: U.S. Pat. No. 1,811,181 (an original disclosure of an open RBC, issued in 1931); U.S. Pat. No. 1,947,777 (an enclosed heat exchanger, adsorption unit, issued in 1934); U.S. Pat. No. 3,630,366 (the typical open conventional RBC, issued in 1971); U.S. Pat. No. 3,704,783 (an aerated fixed film RBC, issued in 1972); U.S. Pat. No. 3,904,525 (a pre-aerated spray RBC issued in 1975); U.S. Pat. No. 4,115,268 (an open or closed RBC with an alternative rotor design, issued in 1978); U.S. Pat. No. 4,137,172 (an attached growth RBC with corrugated disks, operating at 40% submergence, issued in 1979); U.S. Pat. No. 4,289,620 (a RBC in combination with an adsorbent, issued in 1981); U.S. Pat. No. 4,330,408 (a partially submerged RBC incorporating suffusing a portion of disc with air, issued in 1982); U.S. Pat. No. 4,345,997 (an RBC with unique disc ribs, issued in 1982); U.S. Pat. No. 4,385,987 (a RBC with alternative structural design of the discs, issued in 1983); U.S. Pat. No. 4,431,537 issued in 1984; U.S. Pat. No. 4,444,658 issued in 1984); U.S. Pat. No. 4,537,678 issued in 1985); U.S. Pat. No. 4,549,962 issued in 1985); U.S. Pat. No. 5,401,398 issued in 1995); U.S. Pat. No. 5,458,817, issued in 1995); U.S. Pat. No. 5,498,376 issued in 1996; U.S. Pat. No. 5,637,263 issued in 1997); U.S. Pat. No. 5,714,097 issued in 1998); U.S. Pat. No. 5,851,636 (ceramic plates) issued in 1998); U.S. Pat. No. 6,071,593 (grooved ceramic packing) issued in 2000); U.S. Pat. No. 6,241,222 issued in 2001); U.S. Pat. No. 6,783,669 issued in 2004); U.S. Pat. No. 7,156,986 issued in 2007); U.S. Pat. No. 8,460,548 issued in 2013); U.S. Pat. No. 4,563,282 (a RBC incorporating microscreens in conjunction with rotating biological contactors that are placed in a primary settling tank, the aeration tank and a final clarification tank, issued in 1986); U.S. Pat. No. 4,568,457 (an anaerobic RBC incorporating acid and methane phase segments, issued in 1986); U.S. Pat. No. 4,604,206 (a staged anaerobic digestion RBC, issued in 1986); U.S. Pat. No. 4,668,387 (an aerated, completely submerged air-driven RBC, issued in 1987); U.S. Pat. No. 4,692,250 (a recirculating staged waste water treatment RBC, issued in 1987); U.S. Pat. No. 4,721,570 (a RBC with a solids contact zone, issued in 1988); U.S. Pat. Nos. 4,729,828 and 4,737,278 (a modular rotating biological contactor apparatus, issued in 1988); U.S. Pat. No. 5,326,459 (a two-stage RBC with different diameter discs, issued in 1994); U.S. Pat. No. 5,395,528 (a complex sewage treatment apparatus incorporating a RBC, issued in 1995); U.S. Pat. No. 5,407,578 (a partitioned RBC capable of addressing toxic inputs, issued in 1995); U.S. Pat. No. 5,853,591 (a hydraulically driven RBC, issued in 1998); U.S. Pat. No. 6,403,366 (a rotating biofilter scrubber for removing air pollutants, issued in 2002); U.S. Pat. No. 7,083,720 (a modular expandable RBC, issued in 2006); U.S. Pat. No. 8,191,868 (a Rotating Inverse Biological Contactor (RIBC), issued in 2012); and U.S. Pat. No. 8,398,828 (an RBC incorporating photocatalytic degradation with UV light, issued in 2013). Relevant U.S. patent applications include: No. 20050133444 (self-cleansing media, filed in 2005); a patent application for a double-sided, self-cleaning media, filed in 2007; No. 20080053880 (configurable RBC application, filed in 2008); No. 20080210610 (RBC that could be inoculated with various bacteria, filed in 2008).
The patent history displays a wide variety of configurations and arrangements for the aerobic or anaerobic treatment of wastewater through the retained growth of a bacterial biofilm on the RBC rotating surface in open or enclosed reactors. A large heterotrophic, as opposed to autotrophic biomass population is achieved, but gases are not managed and stripping of end products has not been practiced.
U.S. patent application Ser. No. 13/373,860 of Burke, entitled Ammonia Nitrogen Recovery Through a Biological Process, filed on Dec. 1, 2011, disclosed use of a biofilm in a rotating photobioreactor (RBC) to support bicarbonate consumption through the growth of autotrophic organisms, thereby increasing the pH and shifting ammonium to ammonia gas for subsequent stripping. That application claimed a process whereby the pH was increased and the ammonia gas stripped in the same reactor without the use of chemicals, as shown in FIG. 2. Ammonia gas was produced and stripped, thereby reducing end-product inhibition while maintaining concentrated biomass for maximum ammonium to ammonia conversion. The configuration specified in U.S. patent application Ser. No. 13/373,860 has many other applications, some of which are the subject of the present invention. Important benefits of the process include the support of a large retained biomass population as a fixed film, removal of inhibitory end products while they are produced, ease of harvesting the biomass, and low energy inputs.